The present invention relates to color display tubes and particularly to such a tube that is easily miniaturized.
Conventional color display cathode ray tubes such as used in television receivers and computer display monitors ordinarily employ three electron guns, one associated with each of the primary colors. A perforated shadowmask located between the electron guns and areas of colored light emitting phosphors on the tube faceplate defines beam paths between the electron guns and the phosphor areas. The openings in the shadowmask are carefully aligned to allow only electrons from a particular gun to pass through and strike a corresponding color area; however, there are always problems of misconvergence with the complex three gun construction. An electron beam may have the correct angle to address only its color at the center of the screen, but it may have a somewhat different angle near the edge of the screen. The tube's deflection yoke does not deflect each electron beam to the same extent so the center of deflection appears to shift. Slots in the shadowmask must be made narrower than theoretically desirable, or significant dead regions must be established between phosphor areas in order to maintain color purity. These expedients reduce efficiency and brightness of the display.
The aforementioned problems are particularly troublesome with regard to miniaturized color television tubes desired for monitors or view finders of video cameras, and for "virtual environment" applications wherein it is sought to generate realistic full color stereoscopic images of a simulated environment. Resolution problems attributable to registration and convergence become nearly insurmountable in the case of a miniaturized, high resolution color tube and moreover the mere presence of three electron guns makes the device difficult to miniaturize. Therefore, most presently available miniature cathode ray tubes generate only black and white displays.
Beam index tube technology has been employed for the purpose of utilizing only one electron gun in a color tube, wherein the screen includes four phosphor components--the three primary colors plus one which produces ultra-violet light detected by a sensor. Although this concept is well known and would appear to enhance image brightness since the shadowmask is not employed, resolution is disappointing in the case of miniature tubes and the circuitry for driving the tube is complicated.